The field of prosthetic devices has advanced greatly through the years. Many current lower-limb prosthetics use sensors, microprocessor controllers, and valves or other actuators to assist the user's gait motion. The devices range from prosthetics which actively propel the user forward to devices which assist in controlling the motion of the joint. Even if the device does not provide powered motion such as actively propelling the user forward, they may still use energy when in motion to run the valves or other actuators that control the motion of the joint(s). Many of these devices require a power source to operate. The required energy is provided by an onboard battery with a fixed capacity. This battery is limiting to the user because it must be recharged periodically. Many users need to recharge a prosthetic limb daily, although a very active user could conceivably completely discharge the limb in less than a day. Energy harvesting, which is in its infancy in prosthetics, would alleviate the user of this inconvenience.
One issue encountered when designing energy harvesting devices for prosthetics is that only a small amount of deflection is tolerable in a prosthetic limb, therefore limiting the amount of mechanical movement available to move an electromechanical generator as a means of gathering energy. The generator could be directly coupled to the deflecting components, for instance through a series of gears, but the amount of force on some of the components in such a device is often too large for the small electromechanical generator components that can be used in prosthetics, and these high forces can be a significant noise source.
What is currently lacking in the art is an energy harvesting device capable of amplifying the small amount of deflection available when a prosthetic limb is in use to generate a larger mechanical motion that can be used to drive an electromechanical generator while reducing the force exerted on the electromechanical generator. By adding this energy harvesting capability it is possible to partially or fully recharge the existing battery during use. This can greatly extend the time interval between complete recharges reducing the user's need to replace the battery or to plug the device in to recharge the battery. Indeed, if enough energy is harvested, it would not be necessary to recharge at all.